2-aryl malonamide compounds are a class of intermediates in the organic synthesis, for example, 2-(2,6-diethyl-4-methylphenyl) malonamide is an important intermediate in the preparation of a highly-effective herbicide Pinoxaden (WO 00/78881, WO 00/78712).
Currently, the 2-aryl malonamide compounds are mainly prepared through the hydrolyzation of 2-aryl malononitrile compounds (WO 00/78712). However, this method has the defect of difficulty in preparing the 2-aryl malononitrile compounds, especially the more sterically-hindered 2-(2,6-disubstituted aryl) malononitrile. The most effective method of synthesizing 2-(2,6-disubstituted aryl) malononitrile is to use the corresponding aromatic amine as a raw material, which sequentially undergoes diazotization-halogenation (Sandmeyer) reaction and metal-catalyzed C—C coupling reaction to form the 2-(2,6-disubstituted aryl) malononitrile (WO 2004/050607). However, in order to achieve an ideal yield of the metal-catalyzed coupling reaction, an expensive bromine or iodine compound is required to be used as a halogenating agent in the diazotization-halogenation reaction. The diazotization-halogenation reaction will produce large amount of waste pollution, and also leads to safety and halogen corrosion problems. Moreover, the organometallic catalyst used in the metal-catalyzed C—C coupling reaction between the sterically-hindered aryl halide and the malonic acid derivative is expensive and difficult to be recycled.
The inventors of the present invention, through continuous research and exploration, have surprisingly developed a method for preparing 2-aryl malonamide compounds directly from raw materials of 2-(cyclohexenylidene) malononitrile.